The spiral which can be seen on the CRT's to
the left is a special kind of accelerating anode
called a Post Deflection Anode (PDA).
By deflecting before acceleration, much higher
sensitivity could be obtained because the
beam, still travelling slowly, spent more time
between the deflection plates. A special
anode was needed for this with a distributed
potential, to get the least distortion the anode
was a thin spiral of graphite with the potential
applied between the ends of the spiral which
was wound from the screen to the electron
gun in the neck.